This invention is related generally to the art of simulating an environment of electromagnetic signals for the purpose of testing or training on a receiver, and more particularly relates to the simulation of a field of radar signals for the purpose of testing, training and simulating an emitter library on a radar warning receiver.
A commonly used radar warning receiver includes a down converter connecting its antennas to an intermediate frequency superheterodyne receiver. The receiver is scanned across a frequency range of interest either manually or by an electronic scanning system. Detected signals at the output of the receiver are applied to video sections for conversion, processing and display. The type, direction and other characteristics of each radar emitter having a frequency within the scanned range is displayed.
In order to test such systems, and also to train operators on them, systems and techniques have been developed for simulating a field of radar signals which are applied to the receiver. A complete simulation is complex, primarily because of the many variations between different types of radar emitters. Some emit periodic pulses of radio frequency energy, some random pulses and others operate on a continuous wave. Pulse type emitters vary as to the width of the pulse, the interval of pulse recurrence and scheduled changes in this interval. Others even vary in frequency of their emitted signal. Most utilize a scanning antenna, thus requiring the simulation of gain patterns of the emitter and scan rates. Gain patterns for the receiver antennas also need to be simulated. And if the emitter and/or receiver are in vehicles, such as boats or airplanes, which are moving, the relative aspect and changing location need to be simulated as well.
One technique used for simulation is to generate with a separate oscillator and modulator each of the radar emitters to be simulated in a given radar field. This brute-force approach does provide all of the desired signals. But a significant disadvantage is the very large amount of electronic equipment that is required in order to simulate a realistic number of emitters, and the technical problems of combining them.
Another approach that has been suggested to limit the amount of hardware required is to use a lesser number of oscillators and time share them by rapidly switching their frequency and the character of modulation in a manner to appear to simultaneously generate each of the radar signals over a frequency range of interest. A significant disadvantage of this technique is that the repetition rate of pulses sought to be simulated from a given emitter is limited. If a large number of signals are sought to be simulated, the repetition rate of any one signal has to be very low. Also, this technique cannot simulate a continuous wave signal and cannot simulate two pulses from different emitters at the same instant in time. Even with these limitations, however, this technique has enjoyed wide popularity. Each of the aforementioned techniques apply the signals to the radio frequency portion of the receiver.
A third technique is to simulate the signals in a manner that they may be inserted in the digital and video section of the receiver, bypassing the tuner. This has the disadvantage that it tests only a portion of the receiver; it provides only simplified, partial simulation and an operator of the receiver for training purposes does not have an opportunity to operate the tuning portions of it. It is not a real life simulation.
Therefore, it is a primary object of the present invention to provide a technique and system for generating a plurality of signals at different frequencies over a given frequency range, without the limitations of other techniques discussed above, in a real life simulation of an environment of electromagnetic signals and a realistic verification of an emitter library.